1H measurements of the binding of 9 amino acridine to di and tetranucleotides of defined sequence are proposed to investigate 1) the sequence selectivity in binding by this agent in vitro, 2) the existence of site exclusion in very short chains and 3) the actual structure of complexes in solution using spin-labelled agents. Covalent reactions by active agents (psoralen and light or NAAAF) are being studied using oligonucleotides of defined sequence in order to establish the characteristics of frameshift mutagenesis in more detail.